Decoding METARs TAFs and AIRMET

Introduction
In the word of aviation, it is helpful to convey a lot of information quickly. One of the ways they do this is through the use of abbreviations. One of the ways that these abbreviations really go crazy is through METARs (MEteorlogical Terminal Aviation Routine) and TAFs (Terminal Aerodrome Forcast), which are best described as fancy weather reports that include everything a pilot will need to know. With a lot of abbreviations, there needs to be a set format that everyone knows to understand the information conveyed. In many cases the basic set format is as stated:

Location - Date and Time - Wind conditions - Visibility - Temperature - Pressure - and then extra information.

This will be the METAR that will be decoded, the TAF is underneath the METAR and will be covered second


Decoding and Discussion

METAR:



When decoding a METAR it is helpful to remember how the information is presented, first up is the location. This is given as the callsign of the airport that released the METAR, In this case, it comes from the Purdue airport known as KLAF. The next block of numbers 081554Z is the date and time of the report. The date is the first two 08 for the 8th of November (the current month). The next 4 and the Z is the time it was taken in Zulu time (hence the Z), so it is 15:54 Z. Zulu time is also known as Universal Time Coordinated or UTC time (UTC is 5 hours ahead of eastern time to give a more general reference). The next number block 25004KT states the direction of the wind and the speed in knots (KT) so it is coming from 250 degrees at 04 knots. The block after is visibility, which is given as this 10SM CLR, as it is given it says the visibility is 10 statute miles and that it is clear (CLR).

The next two parts of the info given are the temperature/dewpoint and the altimeter setting. In this case, it is given as M02/M09, typically an M wouldn't be included but in this case, there was cold weather and M indicates a negative temperature, M02 means that the temperature is minus 2 degrees celsius, and M09 is the dewpoint and is at minus 9 degrees celsius. Altimeter setting is given as A3051, the letter can be either A or Q and that is the measurement that is used. "A" denotes inches of mercury (Hg), and "Q" is hectopascals (hPa) or millibar (mb) as they both are the same. In this case, it is given as A3051, for this measurement a decimal goes in the middle of the 4 numbers, making this specific measurement 30.51 inches of Hg.

Finally, there is the remarks section, indicated by RMK, everything after this is extra information that doesn't have a specific spot in the METAR already. After RMK it states A02, which means that the METAR was done by specialized automated equipment that CAN tell the difference between rain and snow, if it was A01 it wouldn't be able to tell the difference and a pilot would need to take that into consideration if they were flying into an airport with A01 equipment. The final thing that is stated is SLP338 which is Sea Level Pressure in millibars (mb) or hectopascals (as stated earlier they are equal). This is probably the hardest part to decode as it can get a little complicated. To start place a 10 or 9 before the first digits (338), a 9 will be used if the 3 digits are greater than 500, in this case, because 338 is less than 500 it gets a 10 in front. The last digit is also a decimal, so to properly state that final number it is 1033.8 mb (or hPa).  Using all the information that is given through this METAR you have all the information needed to understand the weather around a specific airport.

TAF:


The TAF is a forecast for the day. The first part is the same as a METAR, it gives the location, KLAF, and the date/time in UTC, Nov 08th at 11:25 UTC (081125Z), the other part 0812/0912 is how long the TAF is valid for (starts at Nov. 08 at 1200 UTC and ends at Nov. 09 at 1200 UTC). The next portion to touch on is the forecast change indicators, stated in their own separate lines. The three that are listed in the TAF are as stated: FM081700, FM090000, and FM091000. These are forecasts and are read similar to a traditional date and time on a METAR but the FM means from. This is to tell anyone listening to the TAF the predicted conditions from that date and time. There are three types of change indicators, FROM (FM), BECOMING (BMCMG) and TEMPORARY (TEMPO), from means, that there will be a rapid change, usually occurring within less than an hour. Becoming is used when a gradual change is expected and is given when the change is going to take about two hours and is stated as BMCMG 1416, for example, the 4 numbers are actually 2 times (as minutes arent that important) 1400 UTC and 1600 UTC. Finally, there is a temporary group which is used if a condition is expected to rise and is expected to not last more than an hour, this is used mainly if there is a given state of the weather and the state might pass into another level occasionally at a few points within a TAFs forecast. and example of which can be SCT030 TEMPO 1923 BKN030, to decode it means that there is expected scattered clouds at 3,000ft and they will temporarily become broken cloud cover at 3,000ft between 1900 UTC and 2300 UTC (Cloud coverage and density will be discussed later, so just understanding the basics of what TEMPO means is okay for now)

Back to the top line, it's onto the wind, and just like a METAR, it is given as direction it's coming from and then speed in knots, so 32005KT is translated as 320 degrees and 5 knots. VRB is also used in the forecast part, stated as VRB03KT, this just means that the wind is coming from a varied wind direction and not a specific degree value.

The next part is visibility, and again it's stated just like a METAR in statute miles (SM), what's not like a METAR is that it is only stated up to 6 SM, anything greater is given a P to denote. For each of the "from" portions and the top portion, visibility is at greater than 6 SM or P6SM. The last portion of this is the cloud condition. The way this is done is to consider the sky in 1/8ths. Clear is 0/8ths of the sky is covered, FEW is 1-2 eighths covered, Scattered (SCT) is 3-4 eighths, broken (BKN) is 5-7 eighths and finally overcast (OVC) is when the whole sky is covered with clouds. They are listed with numbers after them to tell pilots what level the clouds are at in feet. To translate two zeros are needed to be put after the numbers, so if the TAF read FEW250 it would mean there were few clouds at 25,000 ft. The final part of the TAF is an amendment or AMD, and everything afterward is describing the amendment. In this particular case, the amendment is limited (LTD) to cloud visibility and wind until Nov. 9th at 1400 UTC.

Airmet:

An Airmet is an area that is around airports and states a specific type of condition in that area. Figure 1 here is a view from SkyVector, a website that offers a digital sectional chart and can overlay Airmets to visually see the areas affected and not have to just make sense of the block of text that is an Airmet (see figure 2)

Figure 1

Figure 2

To go through the text version of an airmet (where you'll get all the information) it is similar to a METAR or TAF but a little different. The airmet that will be decoded is the large green one in figure 1. Green is for turbulence, the light blue is icing effects, purple (in the bottom corner) is instrument flight rules and one that isnt in the image but is used is pink and that means mountain obstruction. The first part of this airmet is where it came from and is reported from a few different airports at a specific time. This airmet is stated as an update for turbulence and low-level wind shear and is valid until Nov. 8th at 2100 UTC. The next large block of text underneath is the description of areas affected based on airports and states. First, it lists states affected in their two-letter abbreviations, then goes through and lists it via airports with their abbreviated names. After that block of text, the reader of the airmet comes to the next series of red text stating that there is moderate turbulence, in this case, it is specifically between 2 flight levels, 27,000ft and 37,000ft (just like in METARs you need to add two zeros to the end to get the flight level in ft). It again lists that the condition is continuing beyond 2100 UTC and are expected to end sometime around 0000 and 0300 UTC and it is valid from 2100 to 0300 UTC.

Conclusion

Being able to be given a METAR, TAF or Airmet and decern information from them can be both really helpful and determine if the flight will be both successful and safe. If conditions are too rough outside for a UAS platform it can be quickly discerned from an experienced pilot reading a METAR. A TAF is really important too as it states a forecast, and how quickly the conditions are expected to change. Airmets lastly isn't as important as the previous two, they typically are for much higher altitudes that no UAS platform will legally be flying at. Although they can still give important information like mountain obstruction and icing conditions, still it can be a factor in flying the UAS platform. A METAR and TAF together can really tell a UAS pilot everything they need to know to have a safe flight and not pose a danger to bystanders and aircraft alike.